The present invention relates to methods for treatment of cellulosic fibers, particularly textiles and most particularly cotton fabrics, to achieve scouring and dyeing using a single-bath method.
The processing of cellulosic material such as cotton fiber into a material ready for garment manufacture involves several steps: spinning of the fiber into a yarn; construction of woven or knit fabric from the yarn; and subsequent preparation, dyeing and finishing operations. The preparation process, which may involve desizing (for woven goods), scouring, and bleaching, produces a textile suitable for dyeing.
A. Scouring: The scouring process removes much of the non-cellulosic compounds naturally found in cotton. In addition to the natural non-cellulosic impurities, scouring can remove residual manufacturing introduced materials such as spinning, coning or slashing lubricants. Conventional scouring processes typically utilize highly alkaline chemical treatment, which results not only in removal of impurities but also in weakening of the underlying cellulose component of the fiber or fabric. The chemical scouring is followed by extensive rinsing to reduce the risk of re-depositing impurities. Insufficient rinsing yields alkaline residue and uneven removal of impurities on the fabric, which in turn results in uneven dyeing in the subsequent process. Furthermore, chemical scouring creates environmental problems in effluent disposal, due to the chemicals employed and the materials extracted from the fibers. A superior method involves the use of enzymes, particularly pectinases, for scouring, as disclosed, e.g., in U.S. Pat. No. 5,912,407; Hartzell et al., Textile Res. 68:233 (1998); Hsieh et al., Textile Res. 69:590 (1999); Buchert et al., Text. Chem. Col. and Am. Dyestuff Reptr. 32:48 (2000); and Li et al., Text. Chem. Color. 29:71 (1997).
B. Dyeing: Dyeing of textiles is often considered to be the most important and expensive single step in the manufacturing of textile fabrics and garments. The major classes of dyes are azo (mono-, di-, tri-, etc.), carbonyl (anthraquinone and indigo derivatives), cyanine, di- and triphenylmethane and phthalocyanine. All these dyes contain chromophore groups, which give rise to color. These chemical structures constitute several cellulosic dye classes, i.e. vat, sulfur, azoic, direct, and reactive dyes as defined in the Colour Index. Three of these dye types involve an oxidation/reduction mechanism, i.e., vat, sulfur and azoic dyes. The purpose of the oxidation/reduction step in these dyeing procedures is to change the dyestuff between an insoluble and a soluble form.
Processing and dyeing procedures are performed in either a batch or continuous mode, with the fabric being contacted by the liquid processing stream in open width or rope form. In continuous methods, a saturator is used to apply chemicals to the fabric, after which the fabric is heated in a chamber where the chemical reaction takes place. A washing section then prepares the fabric for the next processing step. Batch processing generally takes place in one processing bath whereby the fabric is circulated through the bath. After a reaction period, the chemicals are drained, fabric rinsed and the next chemical is applied. Discontinuous pad-batch processing involves a continuous application of processing chemical followed by a dwell period, which, in the case of cold pad-batch, might be one or more days.
Regardless of whether batch, continuous, or discontinuous pad-batch methods are used, scouring and dyeing steps have not heretofore been compatible; consequently, it has been necessary to rinse or otherwise treat the fabric or to replace the treating solutions between scouring and dyeing. Thus, there is a need in the art for harmonization of scouring and dyeing methods so that they can be performed in a single bath, whether simultaneously or sequentially, so as to shorten processing time, conserve materials, and reduce the waste stream.
The present invention provides methods for single-bath bioscouring and dyeing of cellulosic fibers. The methods are carried out by contacting the fibers with (i) a bioscouring enzyme, and (ii) a dyeing system; by adding the bioscouring enzyme and the dyeing system to the same solution that contacts the fibers. The bioscouring enzyme and the dyeing system may be added substantially simultaneously to the solution containing the fibers. Alternatively, the fibers are (i) contacted with the bioscouring enzyme, for a sufficient time and under appropriate conditions that result in effective bioscouring, after which (ii) the dyeing system is added directly to the solution containing the fibers and the bioscouring enzyme.
Bioscouring enzymes useful in practicing the present invention include, without limitation, pectinases, proteases, lipases, and combinations thereof.
The dyeing system may comprise one or more of direct, reactive, vat, sulfur, or azoic dyes. Alternatively, the dyeing system may comprise: (a) one or more mono- or polycyclic aromatic or heteroaromatic compounds, which function as dye precursors and/or as enhancers or mediators; and (b) (i) an enzyme exhibiting peroxidase activity and a hydrogen peroxide source or (ii) an enzyme exhibiting oxidase activity on the one or more mono- or polycyclic aromatic or heteroaromatic compounds.
Preferably, at least about 30% by weight of the pectin in the fibers is removed by the bioscouring enzyme; more preferably, at least about 50%, and most preferably, at least about 70%, is removed. Furthermore, using the methods of the invention, satisfactory uniformity of dyeing (as measured by visual examination) is achieved. Dyeing fastness properties such as washing fastness, light fastness and crocking (wet and dry) fastness are preferably at least about 3.0 on a color gray scale (Method EP1 in AATCC Technical Manual, vol. 7, 1995, p.350), more preferably above 3.5, and most preferably above 4.0.
In one embodiment, the fibers are contacted with 2000 APSU/kg fabric of pectate lyase at pH about 8, 55xc2x0 C. for about 20 minutes, in the presence of both about 22 gram/l sodium salt and 2% on weight of good (% o.w.g.) of reactive dye in the solution. The color uptake of the fiber is further enhanced by raising the pH using sodium carbonate.
In another embodiment, the fibers are contacted with 2000 APSU/kg fabric of pectate lyase at pH about 8, 55xc2x0 C. for about 30 minutes in the presence of about 22 gram/l sodium salt, about 0.02 g/l chelator (sodium tetraethylenediaminetetraacetate), and 2% o.w.g. of reactive dye. The dye uptake onto the fibers is enhanced by raising the pH using sodium carbonate.
In another embodiment, the fibers are contacted with 2000 APSU/kg fabric of pectate lyase in 2 mM borate buffer pH9, 55xc2x0 C. for 20 minutes. Sodium salt and a reactive dye are added subsequently, after pH is lowered to about 7.5 or lower. The dyeing is then carried out at 60xc2x0 C. for 30 minutes and dye uptake is enhanced by raising the pH of the solution using sodium carbonate.
In another other embodiment, the fibers may also be contacted with additional enzymes, including without limitation other pectin-degrading enzymes, proteases, lipases, and cellulases, alone or in combination with each other or with pectate lyase.
The methods of the invention can be used for treating crude fibers, yarn, or woven or knit textiles. The fibers may be cotton, linen, flax, ramie, rayon, hemp, jute, or blends of these fibers with each other or with other natural or synthetic fibers.